A wireless charging device using Qi standard transmits power in a manner of 2FSK (Binary Frequency-Shift Keying), and a signal received by an energy receiving terminal in the wireless charging system is an inductively coupled signal, such that the signal it received is not a single frequency sinusoidal signal, but may be doped with a large amount of high frequency noise. Currently, since the wireless charging technology is in its early stage, there are not many FSK (Frequency-Shift Keying) signal demodulation circuits for the Qi standard wireless charging device. The existing FSK demodulation circuits are all directed at ordinary FSK signals, and the traditional 2FSK demodulation methods are mainly three manners: coherent demodulation, filtering non-coherent demodulation and quadrature multiplication non-coherent demodulation.
In the Qi standard communication protocol, a period difference between a carrier frequency Fop and a modulation frequency Fmod is specified in order to achieve the transmission energy stability, and its maximum value is 282 ns and its minimum value is only 32 ns. If the traditional method is used for demodulation, the entire system needs very high precision to distinguish different frequencies, which will greatly increase the overhead of the entire circuit no matter adopting the analog or the digital method. Meanwhile, the carrier frequency Fop may be an arbitrary value in a range from 110 KHz to 205 KHz in different communication phases of the same system, thereby further greatly increasing the overhead of the entire demodulation circuit.